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The application is described of a modified X‐ray diffraction method (Auleytner technique with an extreme back reflection arrangement) to the study of lattice parameter variations caused by proton irradiation of GaP single crystals. This method allows a simultaneous investigation of several differently irradiated spots on the crystal surface and provides the whole spectrum of strain values, reflecting the depth dependence of the radiation damage. An experiment with a bevelled GaP surface confirms the supposed correspondence between strain magnitude and crystal depth. For the low dose region the coexistence of expansion and compression is established and a preliminary explanation of the transition to the regime of pure expansion is given. The results obtained are compared with those from two‐crystal diffraction and Kossel measurements and a good agreement is found. First results concerning other semiconductors are briefly reported.

The asymmetrical Bragg case of X-ray diffraction on a thick real crystal is theoretically investigated on a layer model containing dynamically diffracting mosaic blocks. By means of this theory the experimental dependence of the integrated reflectivity Ri on the asymmetry angle a deviating from the kinematical formula may be understood as 8 result of extinction-and absorption processes inside the mosaic crystal. Thus the remarkably thick surface layers or surface protuberances assumed b y MATHIESON and in previous papers for the interpretation of the experimental &(a) become needless or they are considerably thinner. respectively? indeed. -On the base of the represented theory the determination of special (model-dependent) characteristics of the dislocation network is possible r i a absolute Ri(a)-measuring values.

Selition Physik der Technischen Universitht Dresden (a) und VEB Freiberger Prhziaionsmechanik (b)ZumExperimental data, a lack of satisfactory theorebical discussion, and some practical problems (application of crystal monochromators, analysis of real structure) as well demand an improvement of the theory of integrated reflectivity, R , , and of polarization ratio, p , in case of X-ray diffraction in thick real crystals (symmetrical Bragg case).Relatively simple expressions have been obtained concerning the diffraction process in a layer model containing dynamically diffracting mosaic blocks. They fit experimental results, especially the maximum of p a t average crystal quality. The theory yields for that maximum p = I/lcos 201 in case of strong primary and secondary extinction. This is, obviously, in better agreement with experimental work using ordinary monochromator crystals than expressions of the type p = cos2 2 0 or Icos 201 or averages of them.